Drive unit for tracked vehicle and vehicle provided with drive unit

ABSTRACT

The invention relates to a drive unit for a tracked vehicle such as a tracked forwarder. The drive unit comprises a track support beam, at least one drive wheel, a set of support wheels and an endless track, said at least one drive wheel being arranged to drive said endless track running over said at least one drive wheel and said set of support wheels. The drive wheel and the support wheels are rotatably attached in said track support beam. The drive unit further comprises an electric motor attached to said at least one drive wheel and integrated in said track support beam, and a track support beam integrated lubrication system comprising a pump unit arranged for pressurized supply of lubricant to parts of the drive unit in need of lubrication.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 14/787,674, a U.S. National Stage patentapplication, filed on Apr. 24, 2014, which claims priority toInternational patent application PCT/SE2014/050496, filed on Apr. 24,2014, which claims priority to Swedish Patent Application No. 1350563-1,filed on May 8, 2013, the entire contents of which are incorporatedherein by reference.

FIELD OF THE INVENTION

The present invention relates to a drive unit for tracked vehicle. Thepresent invention also relates to a vehicle such as a tracked vehicle.

BACKGROUND OF THE INVENTION

Track driven/tracked and wheeled vehicles of today are typically drivenby drive systems/powertrains mainly based on fuel engines.

This also applies for forestry vehicle such as forwarders or harvesterswhich today typically are wheeled. The fact that most forestry vehiclesare wheeled depends on that the opinion since the sixties was that thesewere felt to be more reliable than tracked vehicles. This has latelybeen started to be questioned as tracked vehicles e.g. facilitate lowerimpact on the ground, i.e. degradation of the ground.

In order to transfer the power from the fuel engine of a vehicle forcreating drive torque of a wheel or track a large amount of gears,shafts, gear wheels, chain wheels or similar power transmittingcomponents are typically needed which all need lubrication, maintenanceand space. These components may also limit aspects such as e.g. groundclearance and how vehicle geometries may be constructed. Fuel enginesalso typically have a low efficiency.

These disadvantages results in vehicles of today including trackedvehicles being unsuitable for a number of different applications wherethere are demands on reliability in operation/environmentalfriendliness. This especially applies for tracked vehicles intended forforestry such as forwarders or harvesters which typically are operatedday and night in multi-shifts and where losses of production caused byvehicle errors result in great financial consequences as the entirechain of logistics is affected. Today you go more and more towards socalled “cut-to-length” logic within forestry which means that forwardersat the felling site cuts up timber based on information from clientsregarding desired quantity, size and length. The timber is marked on thesite and is then transported by a forwarder to a collection point wherea timber vehicle such as a truck collects the timber and transports thisfurther to the client such as a sawmill or a process industry. Thiscombined with just-in-time logic results in a fall in production causedby error stand still of harvester or forwarder affecting all subsequentlinks in the logistics chain. Further the environment where thesevehicles operate, i.e. felling sites and timber collecting sites, arelocated far away from service centres and/or service technicians whichresults in that it takes long time before service can be carried throughby technicians on the site or in a workshop.

Consequently there is a need to present improvement within drive systemsfor tracked vehicles.

An object of the present invention is to provide a drive unit for atracked vehicle which has low weight.

An additional object of the present invention is to provide a drive unitwhich is robust and has few moving parts.

An additional object of the present invention is to provide a drive unitfor a tracked vehicle which is compact and takes up a small volume.

An additional object of the present invention is to provide a drive unitfor a tracked vehicle which facilitates high operational reliability andefficiency for creating low operative expenses.

Another object of the present invention is to provide a drive unit for atracked vehicle which facilitates service and maintenance.

An additional object of the present invention is to simplify service andmaintenance of a in the tracked vehicle comprised track support beam andthe components being parts thereof.

SUMMARY OF THE INVENTION

These and other objects, apparent from the following description, areachieved by a drive unit for tracked vehicle and e vehicle which are ofthe type stated by way of introduction and which in addition exhibitsthe features described below. Preferred embodiments of the drive unitand the vehicle are defined below.

According to an embodiment a drive unit for tracked vehicle is provided,wherein the drive unit comprises a track support beam, at least onedrive wheel, a set of support wheels and an endless track, said at leastone drive wheel being arranged to drive said endless track running oversaid at least one drive wheel and said set of support wheels. The atleast one drive wheel and said set of support wheels are rotatablyattached to said track support beam. The drive unit further comprises anelectric motor attached to said at least one drive wheel and integratedin said track support beam, and a lubrication system integrated in thetrack support beam and comprising a pump unit arranged for pressurizedsupply of lubricant to parts of the drive unit in need of lubrication.

Hereby is facilitated a drive unit for a tracked vehicle whichfacilitates driving of the respective drive wheel of the vehicle andwhere high efficiency is provided by means of utilization of an electricmotor. Further a drive unit with high operational reliability androbustness is achieved when electric motor and lubrication system isintegrated, i.e. confined, and thereby not risking collision withobjects which are passed by the vehicle during operation. Further acompact drive unit with low weight is achieved as structure of the driveunit does not need to be modified in size in order to fit the electricmotor and lubrication system.

Further is hereby provided a track assembly configuration for a trackedvehicle, which track assembly configuration constitute an autonomousdrive unit which may be driven in a reliable way with high performance.To, in addition to electric motor, integrate an active (pressurized)pump system in the track support beam results in the effect thatelectric motor, transmission device and other central components forpropulsion of the track assembly may be given substantially higherperformance and longer life-span than autonomous (self-driving) trackassemblies according to prior art.

The integrated lubrication system typically comprises a lubricationreservoir for storage of lubricant, wherein the pump unit is arranged topump lubricant from said lubrication reservoir to the drive unit partsin need of lubrication.

Further, the integrated lubrication system comprises at least onepressure conduit configured to guide the pressurized lubricant from thelubrication reservoir to the drive unit parts in need of lubrication.

Other advantageous aspects and embodiment of the lubrication systemintegrated in the track support beam are described in the subsequentdetailed description.

According to another aspect the objects are achieved with a drive unitfor a tracked vehicle comprising a track support beam, at least onedrive wheel, a set of support wheels and an endless track. Said at leastone drive wheel and said set of support wheels are rotatably attached tosaid track support beam. Said at least one drive wheel is arranged todrive said endless track running over said drive wheel and said set ofsupport wheels. Said track support beam comprises an electric motorwhich is connected to said at least one drive wheel and integrated insaid track support beam in a longitudinal direction of said tracksupport beam.

According to an embodiment said track support beam of said drive unitcomprises at least one partition plane for uncovering an inner space ofsaid track support beam where said electric motor is integrated.

By providing a partition plane maintenance and service of said electricmotor and the other components confined in said inner space issimplified.

According to an embodiment said partition plane is arranged to besealable by means of a detachable cover arranged to be mounted lyingagainst said partition plane of said track support beam. This simplifiesaccess to said electric motor.

According to an embodiment said at least one drive wheel and saidelectric motor are arranged to be mounted in a front section of saidtrack support beam.

According to an embodiment said track support beam is a skid beam.

According to an embodiment an output shaft of said electric motor isarranged at essentially the same height of said track support beam as adrive shaft of said track support beam, said drive shaft being arrangedto drive said at least one drive wheel.

Hereby a simplified power transmission path from electric motor to drivewheel is achieved which makes the need for moving parts being part ofthe power transmission path low. This creates high operationalreliability and reduces weight since the construction requires fewerparts and that fewer parts are hereby being subjected to wear. Further,reduced need for lubrication is achieved with this solution as fewerparts such as gears, gear wheels reducing this need.

According to an embodiment said drive unit comprises a transmissiondevice integrated in said track support beam such that the axial maindirection of extension of the transmission device is aligned with theoutput shaft of said electric motor.

According to an embodiment said electric motor is connected to a driveshaft arranged to drive said at least one drive wheel, via atransmission device comprising a planetary gear, a transmission shaftand a bevel gear, to which said drive shaft is connected.

According to an embodiment an end of said transmission shaft which isdirected towards said electric motor is arranged to be connected to saidplanetary gear and an opposite end of said transmission shaft which isdirected towards said drive shaft is arranged to be connected to saidbevel gear.

According to an embodiment said at least one drive wheel is constitutedby a drive wheel pair.

According to an embodiment said track support beam of said drive unitcomprises an integrated lubrication system for lubrication.

According to an embodiment said track support beam of said drive unitcomprises an integrated cooling system for cooling.

According to an embodiment said track support beam is configured forattachment to a chassis beam comprising control means for controllingsaid electric motor.

According to an embodiment said electric motor is configured forattachment to a combustion engine via a generator for power supply.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the present invention will be had upon thereference to the following detailed description when read in conjunctionwith the accompanying drawings, wherein like reference characters referto like parts throughout the several views, and in which:

FIG. 1 schematically illustrates a perspective view of a tracked vehiclecomprising drive unit pairs according to an embodiment;

FIG. 2 schematically illustrates a perspective view of a drive unit pairaccording to an embodiment;

FIG. 3 schematically illustrates a perspective view of a track supportbeam according to an embodiment;

FIG. 4 schematically illustrates a perspective view of a centre beamaccording to an embodiment;

FIG. 5 schematically illustrates a diagram of a powertrain according toan embodiment;

FIG. 6A schematically illustrates a side view of a drive unit accordingto an embodiment;

FIG. 6B schematically illustrates a side view of a front section of thedrive unit in FIG. 6A in more detail;

FIG. 6C schematically illustrates a perspective view of a track supportbeam divided along a transversal partition plane according to anembodiment;

FIG. 6D schematically illustrates a perspective view of a front tracksupport beam section according to an embodiment, after partition alongthe transversal partition plane; and

FIG. 7 schematically illustrates a side view of the front track supportbeam and a lubrication system integrated therein according to anembodiment.

DETAILED DESCRIPTION OF THE INVENTION

Herein the term “track support beam” refers to a structural elementarranged to support ground engaging members such as e.g. an endlesstrack.

Herein the term “skid beam” refers to an example of a track supportbeam.

Herein the term “drive unit” refers to a unit capable of bringing theunit and other units attached thereto in movement, i.e. driving theunit.

Herein the term “track assembly” refers to a unit of tracked vehiclescomprising a track support beam, drive wheels and support wheels and acircumferential endless track, said unit being arranged to support anddrive ground engaging members in the form of endless tracks. The term“track assembly” thus relates to an example of a drive unit adaptedtowards application for tracked vehicles.

With reference to FIG. 1 a tracked vehicle 10 according to the presentinvention, provided with a front vehicle unit 11 and a rear vehicle unit12, is shown. Each of the front and rear vehicle units comprises a driveunit pair 60. Said drive unit pair 60 comprises two drive units arrangedon opposite sides of the vehicle. The drive unit is constituted by atrack assembly and are arranged for driving the vehicle. The respectivedrive unit pair is coupled together with an intermediate centre beam,such as a chassis beam. Said centre beam is arranged to support avehicle structure, e.g. in the form of a vehicle cabin, power supplies,load carrying structure and a crane. According to this configuration ofthe vehicle, the centre beam of the front vehicle unit is arranged tosupport a vehicle cabin 15 and a power supply 5, such as an internalcombustion engine, where the internal combustion engine according to oneembodiment is constituted by a diesel engine. According to thisconfiguration of the vehicle, the centre beam of the rear vehicle unitsis arranged to support a load-carrying structure comprising aload-carrying frame 30 and a U-beam configuration 31 for supportingtimber. The load-carrying frame is according to this embodiment alsoarranged to support a crane 44 for loading/unloading of timber. The rearvehicle unit is also arranged to support a crane 32 forloading/unloading of timber.

The exemplified vehicle 10 is a tracked forestry vehicle in the form ofa forwarder intended to transport timber from a harvesting site to acollection site. The vehicle according to the present invention may beconstituted by any suitable tracked vehicle. According to oneembodiment, the vehicle is a harvester intended for cutting timber.

With reference to FIG. 2 a drive unit pair 60 coupled together with anintermediate centre beam is shown. In more detail a drive unit pairintended for a rear vehicle unit is shown, such as said rear vehicleunit 12 exemplified with reference to FIG. 1. The respective drive unitis constituted by a track assembly 20 arranged for driving of thevehicle. Said track assembly comprises a track support beam 22, whichhere is constituted by a skid beam. Said tracks assembly furthercomprises a set of support wheels 23, at least one drive wheel 24, andan endless track 25. Said set of support wheels and said at least onedrive wheel are arranged to be suitably rotatably supported by saidtrack support beam. Said endless track is arranged to run over said atleast one drive wheel and said set of support wheels. Said set ofsupport wheels are arranged in a pair configuration, i.e. the respectivesupport wheel in each pair configuration is arranged on opposite sidesof said track support beam. Said track assembly further also comprisesan electric drive device 3 (shown in FIG. 5) drivingly coupled to saidat least one drive wheel. Said electric drive device 3 is typicallyconstituted by an electric motor.

The exemplified vehicle 10 is a diesel-electric driven vehicle, such asdriven by said electric drive device 3, which is power supplied via agenerator coupled to a combustion engine in the form of a diesel engine.The vehicle may have any suitable power supply for the propulsion of thevehicle. The vehicle is according to a variant hybrid-driven. Thevehicle is according to a variant electrically driven, where poweraccording to one alternative is effected by means of an energy storagedevice such as a battery unit, fuel cell or capacitor unit.

With reference to FIG. 3 a drive unit in the form a track assembly isshown where said endless track for illustrative purposes has beenremoved.

Said track assembly 20 comprises, like said track assembly exemplifiedwith reference to FIG. 2, a track support beam 22, a set of supportwheels 23.

Said track assembly further comprises a drive wheel pair 28 comprising afirsts drive wheel 24 and a second drive wheel 26 arranged on oppositesides of said track support beam. The first and second drive wheels arearranged to be driven by means of a drive shaft 9, defining an axis DArunning transversely through said track support beam. Said trackassembly further also comprises an electric drive device 3 (shown inFIG. 5) drivingly coupled to said at least one drive wheel via saiddrive shaft 9.

Said track assembly further comprises a first cross bar 51 and a secondcross bar 52 configured for attachment via fastening members to a centrebeam 45 (shown in FIG. 4). Said first and second cross bars arecomprised in a suspension device for said track assembly 20 of thevehicle 10.

According to a variant said first and second cross bars are constitutedby an A-arm.

FIG. 4 shows a centre beam 45 arranged for connection to a trackassembly.

Said centre beam is arranged for supporting of vehicle structures. Saidcentre beam comprises attachment points 53 arranged on the underside ofsaid centre beam, said attachment points being configured for attachmentto fastening members 51, 52 (not shown in FIG. 3) of track assembly. Inmore detail said centre beam is arranged for attachment to two trackassemblies, i.e. a track assembly pair, the two track assemblies in thetrack assembly pair being arranged on opposite sides of the centre beamsuch that the centre beam is arranged intermediate to said trackassemblies of the track assembly pair and such that the main directionof extension of the centre beam is essentially parallel to the maindirection of extension of the respective track assembly of the trackassembly pair.

According to a variant said centre beam is constituted by a chassis beamarranged to support chassis structures.

With reference to FIG. 5 a powertrain 2 is shown intended to beintegrated in a track assembly. Said power train comprises an electricdrive device 3. Said electric drive device is configured for drivablecoupling to said drive wheel pairs 24, 26 via a transmission device anda drive shaft 9. Said transmission device is constituted by a planetarygear 6, a transmission shaft 7 and a bevel gear 8. Said bevel gearcomprises a first bevel gear element 8:1 provided with conical gearwheels and a second bevel gear element 8:2 provided with conical gearwheels, said gear wheels of said first and second bevel gear elementsare meshed for power transfer. In more detail one output shaft 81 (shownin FIG. 6B), which transfer torque generated by a rotor of said electricdrive device, is configured for coupling to said planetary gear forpower transfer from said output shaft to said transmission shaft. Saidtransmission shaft is further configured for coupling to said bevel gearfor power transfer from said transmission shaft to said drive shaft.Said drive shaft is further configured for coupling to said drive wheelpair for power transfer from said drive shaft to said drive wheel pair.This results in the output torque from the output shaft of said electricdrive unit to input torque to said planetary gear. Said planetary gearthen transfer torque input to said planetary gear to torque of saidtransmission shaft. Output torque from said transmission shaft is thentransformed to input torque to said bevel gear. The input torque to saidbevel gear is then transformed to input torque to said drive shaftarranged to drive said drive wheel pair. That is, said second bevel gearelement 8:2 is arranged to rotate about said drive shaft 9 and saidfirst bevel bear element 8:1 is arranged to rotate about saidtransmission shaft 7.

According to a variant said powertrain 2 further comprises a pump unit13 arranged to pump oil from a reservoir, (not shown) arrangedintegrated in the skid beam, to parts in need of a lubrication, such asthe planetary gear, the bevel gear, bearings etc. The oil being pumpedfrom the pump may also be supplied to the electric drive device in thepurpose of cooling it and/or providing lubrication of bearings of it.

According to a variant said powertrain 2 further comprises a parkingbrake unit 14 arranged such that when the vehicle is placed in a parkedposition activate a brake function which brakes said electric driveunit. Preferably said parking brake is arranged on a high speed side ofthe powertrain such that the size/weight of the parking brake unit canbe minimized and that the braking force provided by the parking brakeunit can be maximized through gear change.

With reference to FIG. 6A a track assembly comprising an integratedelectric drive device is shown. With reference to FIG. 6B a front partof a track assembly comprising an integrated electric drive device shownin FIG. 6A is shown.

Said track assembly 20 comprises, like the track assembly exemplifiedwith reference to FIG. 2, a track support beam 22, a set of supportwheels 23 and at least one drive wheel 24.

Said track assembly 20 further comprises an electric drive devicearranged integrated in said track support beam. Said electric drivedevice is arranged integrated in a front section of said track supportbeam. In more detail said electric drive device is arranged integratedin said track support beam such that an axis EA defining output shaft 81of the electric drive device is essentially parallel to an axis BAdefining the main direction of extension of said track support beam.That is, the electric drive device is arranged integrated in said tracksupport beam in an essentially longitudinal direction of said tracksupport beam. Said electric drive device is also arranged integrated insaid track support beam at essentially the same height as a drive shaft9 arranged to drive said drive wheels.

According to a preferred variant said electric drive device is arrangedintegrated in said track support beam such that the axis EA isessentially parallel to the axis BA and such that said electric driveunit is arranged integrated in said track support beam at essentiallythe same height as said drive shaft.

According to a variant said output shaft 81 of said electric drivedevice is arranged integrated in said track support beam at essentiallythe same height as said drive shaft.

Said track assembly further comprises a transmission device which isarranged integrated in said track assembly. Said integrated transmissiondevice is arranged to transfer torque generated by said electric drivedevice to a drive shaft 9 arranged to drive said drive wheels 24. Theaxial main direction of extension of said transmission device isarranged aligned with said axis EA defining said output shaft of theelectric drive device. Said transmission device comprises a planetarygear 6, a transmission shaft 7 and a bevel gear 8 (shown in FIG. 5),which is constituted by a first and second bevel gear element 8:1, 8:2.Said transmission shaft is arranged aligned with said output shaft ofsaid electric drive unit. Said output shaft of said electric drivedevice is arranged to transfer torque generated by said electric drivedevice to said planetary gear. An output shaft 82 from said planetarygear is connected to said transmission shaft for transfer of torque fromsaid planetary gear via said transmission shaft to an input shaft 83 ofsaid first bevel gear element 8:1 of said bevel gear. Said first bevelgear element is connected to said second bevel gear element 8:1 fortransfer of torque from said first bevel gear element to said secondbevel gear element 8:2. Said second bevel gear element is connected tosaid drive shaft about which said second bevel gear element rotatesduring torque transfer for transferring torque to said drive shaft. Saiddrive shaft is arranged for connection to said at least one drive wheel,such as said drive wheel pair, for driving of said endless track 25(shown in FIG. 2). This results in that one end of the transmissionshaft, which is directed towards said electric drive device, isconfigured for connection to said planetary gear and in that an oppositeend of said transmission shaft, which is directed towards said driveshaft, is configured for connection to said bevel gear.

Said electric drive device is configured to be attached to a structure19 of said track support beam by means of a suitable joint 11. Saidjoint may according to a variant be constituted by a bolt joint.

For illustrative purposes a configuration of a track assembly onlycomprising one drive wheel is shown in FIG. 6A and in FIG. 6B. it shouldhowever be noted that this configuration may be provided with a drivewheel pair 28 comprising a first and a second drive wheel 24, 26arranged on opposite sides of said track support beam (shown in FIG. 3).

According to a variant said track support beam comprises a partitionplane 40 (shown in FIG. 6b as a hatched area) arranged to uncover aninner space of said track support beam in which space said electricdrive device is integrated. According to this variant said partitionplane is arranged to be sealable by means of a detachable cover arrangedto be mounted lying against said partition plane of said track supportbeam. Said partition plane is arranged in a front section of said tracksupport beam. Said front section is arranged in the front of said tracksupport beam, i.e. in an end of said track support beam being directedin positive drive direction. According to a variant said partition planeis also arranged to uncover an inner space of said track support beam inwhich space said transmission device is integrated.

As is apparent from FIG. 6B the above described partition plane 40 is alongitudinal partition plane which runs in the longitudinal direction ofthe track support beam, which longitudinal direction constitutes themain direction of extension of the track support beam and essentiallycoincides with the direction of travel of the tracked vehicle.

Instead of or in combination with this longitudinal partition plane 40the track support beam 22 is advantageously provided with a transversalpartition plane running transversal to the longitudinal direction of thetrack support beam and essentially perpendicular to the longitudinaldirection of the track support beam. Such a transversal partition planeis in FIG. 6B indicated with a reference number 41.

Also partition planes not being strictly perpendicular to thelongitudinal direction of the track support beam is deemed to fallwithin the scope of what is herein intended with transversal partitionplane. Transversal partition plane should hereby be deemed to refer toany partition plane along which the track support beam 22 may be dividedin what may clearly be deemed to constitute a front 22A and rear section22B of the track support beam 22.

FIG. 6C shows an exemplified embodiment of the transversal partitionplane 41 in FIG. 6b , along which the track support beam 22 isconfigured to be divided in front section 22A and a rear section 22B.The front section 22A is arranged in the front of said track supportbeam 22, i.e. in an end of said track support beam 22 being directed inpositive drive direction. The rear section 22B is arranged in the rearend of said track support beam 22, i.e. in an end of said track supportbeam being directed in negative drive direction.

The front section 22A is substantially smaller than the rear section 22Band thus constitutes a relatively small part of the track support beam22. With “smaller” is here intended at least the length in thelongitudinal direction of the track support beam. The length on thefront section 22A is substantially shorter than half of the total lengthof the track support beam and preferably shorter than a third of thetotal length of the track support beam.

The transversal partition plane 41 is arranged to be sealable by meansof the above mentioned structure 19, which structure in this embodimentconstitutes a detachable sealing cover 19. Said sealing cover 19 isfurther arranged to seal an inner space of the track support beam 22,which inner space is arranged in said front section 22A of the tracksupport beam 22. Said inner space is accessible via the transversalpartition plane 41 by dismantling of said sealing cover 19. The fronttrack support section 22A accommodates the electric drive unit 3, thetransmission device 6, 7, 8 and a in the track support beam integrated22 lubrication system, which will be described in more detail herebelow. At least parts of the electric drive unit 3 and the integratedlubrication system are accommodated in said inner space which isaccessible via said transversal partition plane 41. Since the frontsection 22A of the track support beam 22 integrates the electric motor 3this section 22A will occasionally for the motor comprised section inorder to be able to distinguish it from the rear, non-motor comprisedsection 22B without directional indications.

An advantage with the transversal partition plane 41 is that the front22A and rear section 22B of the track support beam 22 may be dismantledseparately. Thereby service and maintenance of the different componentsof the track support beam is facilitated since only the part of thetrack support beam housing the component/components that need to bemaintained or repaired need to be dismantled and moved. Further in caseof irreparable errors of important system components in the tracksupport beam all or part of the track support beam 22, i.e. the front22A or rear 22B section, housing the irreparable component may bereplaced to an entirely new such part. For example the entire frontsection 22A may be replaced by a new section in case of sever failurearising on e.g. the electric drive unit, the transmission device or thelubrication system. Replacing the entire track support beam 22 is insuch situations difficult or impossible since its weight and size oftenmakes transport of en entire track support beam to the site where thecomponent has failed, particularly since this often is located in aninaccessible forested terrain. Since the electric drive motor 3, thetransmission device 6, 7, 8 and the integrated lubrication system allare integrated in the front section 22A it is likely that a possibleoperation break down of the vehicle 10 is caused by errors of acomponent in said front section 22A. By facilitating easy exchange ofthe entire front section 22A the tracked vehicle 10 may quickly beplaced in service again by delivering a new front section to the failurelocation at the same time as the broken section is taken therefrom formisdiagnosis and repair.

FIG. 6D shows a cross section of the front section 22A of the tracksupport beam along the transversal partition plane 41, with the sealingcover 19 dismantled and exposing said inner space in the front section22A. As is apparent from FIG. 5D and FIG. 7 the inner space of the frontsection 22A is directly accessible via the transversal partition plane41. This directly accessible space comprises a lower chamber 43 and anupper chamber 48, which at least partly are separated by a partitionwall 54. As will be described in more detail the lower chamber 43 of theinner space constitute a reservoir for lubricant in the lubricationsystem integrated in the track support beam 22, which lubricanttypically is constituted by oil. In the upper chamber 48 of the innerspace the electric drive unit 3 is arranged. The sealing cover 19 isconfigured to prevent lubricant from spilling out from said reservoir 43when the front 22A and rear 22B section are separated from each other bydismantling of the track support beam 22. This is provided in that thesealing cover 19 is configured to constitute a removable wall of saidreservoir 43, which seals the reservoir 43 when it is mounted forsealing said inner space of the front track support beam section 22A. Aneffect of the of the design of the sealing cover is that the oilreservoir 43 and therein mounted components of the integratedlubrication system, such as said pump unit 13, are easily accessible viathe transversal partition plane 41, wherein the lubricant which usuallyis accommodated in the reservoir 43 may be tapped out through a tap hole(not shown). An additional effect of the design of the sealing cover isthat it prevents spill of lubricant by dismantling of the track supportbeam 20, which simplifies by replacement or repair of the front 22A orrear 22B track support beam section.

The front 22A and the rear section 22B of the track support beam 22 arethus configured to be detachably mounted to each other. In an embodimentthis detachable mounting is provided by means of a bolt joint. As isapparent from FIG. 6C and partly also 6D the transversal partition plane41 comprises two flanges 44A, 44B, of which one sits on the frontsection 22A and one on the rear section 22B of the track support beam22. Theses flanges 44A, 44B constitute contact surface between the front22A and the rear 22B track support beam section 22. The two flanges 44A,44B are provided with corresponding holes 46 (wherein bolts 47 aremounted in the holes of the front flange 44A in FIGS. 6C and 6D) whereinthe flanges 44A, 44B and thereby the front 22A and rear 22B tracksupport beam section are configured to be detachably mounted to eachother by means of bolt joint.

Further the front flange 43A comprises a milled-out cover planecomprising the surfaces 49A-49C against which the sealing cover 19 isconfigured for detachable mounting. In this exemplified embodiment thecover plane and the sealing cover 19 are provided with correspondingholes for removable joining by means of screwing. In order to sealagainst the inner edge of the front flange 43A against which the outeredge of the sealing cover bears when the sealing cover is mountedagainst the milled-out plane, said outer edge of the sealing cover 19comprises a milled-out track in which an o-ring is mounted forpreventing leakage between the outer edge of the sealing cover and theinner edge of the flange when the sealing cover 19 is mounted againstthe milled-out cover plane.

According to an embodiment said track assembly comprises an integratedlubrication system. Said lubrication system is according to a variantintegrated in said track support beam, such as integrated in said innerspace of said track support beam. The lubrication system comprises apump unit, such as said pump unit 13 exemplified with reference to FIG.5. Said pump unit is connected to a reservoir comprising lubricant, suchas lubrication oil. In more detail said pump unit is arranged to providea flow of lubricant from said reservoir in a lubricationcircuit/lubrication conduit which is connected to parts in need oflubrication, such as said planetary gear and/or parts of said electricdrive device.

According to a variant said lubrication system also comprises a coolingfunctionality. This makes the lubrication oil also providing cooling.According to this variant said reservoir comprising lubrication oil ofsaid lubrication system is arranged to cool said lubricant in that saidlubricant is thrown towards the walls confining said reservoir when saidpump unit pumps lubrication oil around in the lubrication system, i.e.pumps lubricant from said reservoir via said lubricationconduit/lubrication circuit back to said reservoir. Further saidlubrication conduit/lubrication circuit through which lubricant ispumped by said pump unit may be arranged to provide cooling of saidlubricant, i.e. structures of said track support beams which arearranged thermally applied to said lubrication conduit/lubricationcircuit acts as coolers, i.e. cools said lubricant.

A more detailed embodiment of the lubrication system integrated in thetrack support beam 22 will now be described with reference to FIG. 7.

As is apparent from earlier description the tracked vehicle 10 accordingto a preferred embodiment is provided with a track assembly pair 60 ofwhich each track assembly 20 constitute an autonomous drive unit capableto be driven on its own by means of en electric drive device 3, such asen electric motor, integrated in a track support beam 22 of the trackassembly 20. A transmission device for transfer of power from theelectric motor 3 to the drive shaft 9, here comprising a planetary gear6, a transmission shaft 7 and a bevel gear 8, are also integrated in thetrack support beam 20.

That the track assembly 20 constitutes an autonomous drive unit capableof being driven in and by itself means that drive wheel, support wheels,track and other components necessary for propulsion are entirely beingsupported by the track assembly itself. It is shall thereby beunderstood that the track assembly 22 according to the presentdescription does not have any components necessary for propulsionjournaled or in another way supported by a chassis beam, such as thechassis beam 45, or other by the chassis beam supported constructionsconstituting part of a vehicle body to which the track assembly isattached.

In order to reliably be able to drive the tracked vehicle 10 withoptimal performance by means of the autonomous track assemblies 20 eachtrack assembly 20 is provided with an active lubrication system, i.e. alubrication system comprising active components for pumping lubricationmean to components in need of lubrication. Tracks assemblies accordingto prior art possibly comprise passive lubrication system, e.g. in theform of oil bath, but generally do not include any lubrication systemsat all.

The active lubrication system for the respective as drive unitconstituted track assembly 20 is integrated in the track support beam 22of the track assembly. More particularly the lubrication system isintegrated in the front section 22A of the track support beam 22. Asmentioned above the lubrication system comprises a lubricant reservoirfor storage of lubricant, such as lubrication oil, wherein the lubricantreservoir is constituted by the lower chamber 43 of the inner space ofthe front track support beam section 22A. It should in this respect bepointed out that the lubricant reservoir is not constituted by anyseparate container which has been integrated in the track support beam22 but that the lubricant reservoir is constituted by a recess of thetrack support assembly itself, which recess forms said lower chamber 43constituting lubricant reservoir.

The lubrication system comprises a pump device comprising the pump unit13 mentioned earlier and an electric pump motor 56 for driving of saidpump unit 13. The electric pump motor 56 is configured to be driven byseparate electric feed, which means that the electric motor 3 isconfigured to drive the at least on drive wheel 24, 26 and the pumpmotor 56 independent of each other. Further the lubrication systemcomprises a suction conduit 58 and a suction filter 59. The pump deviceis arranged inside the lubricant reservoir 43 and configured to duringoperation be lowered in lubricant stored in the reservoir 43. An effectof the placement of the pump device is that the number of externalconduits and connections are minimized. An additional effect is that thedistances between pump and lubrication spots become short, which resultsshort pressure conduits and low pressure drop, which in turn results inthat the pump unit 13 and the pump motor 56 can be constructedrelatively small.

The pump unit 13 is configured to pressurize the lubricant in order tothen lead out the pressurized lubricant to the different components ofthe drive unit via a pressure conduit 62. The pressure conduit partlyconsists of a pipe which has been attached to the pump unit 13 and runsthrough a hole in the front wall of the reservoir 43.

The remaining parts of the pressure conduit 62 are typically cast ordrilled in the front section 22A of the track support beam 22.

The pressure conduits 62 lead the lubricant out to parts in need oflubrication. These parts comprise at least certain rotating componentsof the planetary gear 6, such as surfaces for meshing of teeth andbearing surfaces, and typically also certain components of the electricmotor 3.

The lubrication reservoir 43 is positioned at the bottom in the fronttrack support beam section 22A and is thus positioned at a lower heightthan the drive unit components that are to be lubricated. Therebylubricant that has been pumped out to these components can be made toflow back to the lubrication reservoir 43 under the influence of thegravitation. Because of this reason the partition wall 54 between theupper chamber 48 housing the electric motor 3 and the lower chamber 43constituting lubricant reservoir 43 provided with at least onelead-through 63, e.g. in the form of one or more holes or tracks,through which the lubricant may flow from the upper chamber 48 to thelubricant reservoir 43. The upper 48 and lower 43 chambers are formed asrecess of castings, wherein the front track support beam section 22A canbe said to constitute a hollow castings construction. The drainage oflubricant from upper to lower chamber is suitably effected through holesin the goods being constituted by floor in the space of the upperchamber 48 where the planetary gear 6 is arranged.

Further the lubrication system is configured to constitute a combinedlubrication and cooling system for drive unit components in need oflubrication and/or cooling, such as the planetary gear 6 and theelectric motor 3. This is provided in that the lubrication reservoir 43is configured for cooling of the lubricant being accommodated in thereservoir. As mentioned above the lower chamber and thus the lubricationreservoir 43 are designed as recesses from castings. The walls or thereservoir are configured to act cooling jacket by at least partly beingarranged in direct contact with surrounding air, i.e. air that is notconfined by the tracked vehicle 10 or any of its components and therebyrisking being heated by operation of the tracked vehicle. These wallsare solid casting walls with good heat conductibility wherefore theouter surface of the walls are cooled by surrounding air by means ofconvection cooling. Thereby heat from the lubricant accommodated in thereservoir will be guided and spread through the walls of the reservoirto surrounding air.

According to an embodiment said electric drive device 3 is arranged forcoupling to a control unit arranged integrated in said centre beam 45shown with reference to FIG. 4. Said control unit is configured forcoupling to a central control unit (not shown), e.g. a central controlunit arranged in the front vehicle unit 11 illustrated with reference toFIG. 1. The central control unit is configured for coupling to athrottle control of the vehicle such as an accelerator pedal, and tosaid control unit. In more detail said central control unit isconfigured for connection to two control units for control of therespective electric drive device integrated in the respective drive unitof said front vehicle unit and rear vehicle unit. This means that saidcentral control unit is coupled via said two control units to allelectrical drive devices being part of the vehicle. Preferably the frontand the rear vehicle unit comprises two electrical drive devices, one inthe left and one in the right drive unit, i.e. track assembly, of thefront and rear vehicle unit respectively. For example a first controlunit (not shown) may be arranged to control said respective electricdrive devices integrated in said drive unit pair of said front vehicleunit and a second control unit may be arranged to control saidrespective electric drive devices integrated in said drive unit pair ofsaid rear vehicle unit based on information generated by said centralcontrol unit. Wherein said first and second control units are arrangedintegrated in said centre beam connecting said drive unit pair of saidfront and rear vehicle unit respectively. According to a variant saidcentral control unit is arranged to control a control unit (not shown)of a generator and a regulation system (not shown) of the diesel engine.According to this variant said generator is arranged to generateelectric power based on power generated by the diesel engine. Furtheraccording to this variant said central control unit is configured forconnection to said control unit of the generator and to said regulationsystem of the diesel engine. This results in that when the driverpresses on the accelerator pedal the pedal position is transferred to arequested drive torque. This is then sent to the control units arrangedto control the respective electric drive device, wherein the controlunits sends out desired level of voltage and current to the electricdrive devices of the respective drive unit.

Said electric drive devices comprises according to a variant an electricmotor. According to a variant said electric drive unit is constituted byany electric drive unit suitable for the application. According to avariant said electric drive device is constituted by an asynchronousmotor. According to a variant said electric drive unit is constituted byan induction motor. According to a variant said electric drive unit isconstituted by a permanent magnet (PM) motor. According to a variantsaid electric drive unit is constituted by an electric motor arranged tobe power supplied with a three-phase alternating voltage, such as a 700Vthree-phase alternating voltage. According to a variant said electricdrive unit is constituted by a three-phase alternating voltage generatedby a generator coupled to a combustion engine5, such as a diesel engineexemplified with reference to FIG. 1.

The foregoing description of the preferred embodiments of the presentinvention has been provided for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise forms disclosed. Obviously, many modificationsand variations will be apparent to practitioners skilled in the art. Theembodiments were chosen and described in order to best explain theprinciples of the invention and its practical applications, therebyenabling others skilled in the art to understand the invention forvarious embodiments and with the various modifications as are suited tothe particular use contemplated.

Below some general aspects of the drive unit and the tracked vehicleaccording to the present description are listed.

Aspect 1: A drive unit 15 for a tracked vehicle 10 comprising a tracksupport beam 22, at least one drive wheel 24, 26, a set of supportwheels 23 and an endless track 25, where said at least one drive wheeland said set of support wheels are rotatably attached to said tracksupport beam, where said at least one drive wheel is arranged to drivesaid endless track running over said drive wheel and said set of supportwheels, characterized by comprising an electric motor 3 which isconnected to said at least one drive wheel and integrated in said tracksupport beam in a longitudinal direction of said track support beam.

Aspect 2: A drive unit according to aspect 1, where said track supportbeam comprises at least one partition plane 40 for uncovering an innerspace of said track support beam where said electric motor isintegrated.

Aspect 3: A drive unit according to aspect 2, where said partition planeis arranged to be sealable by means of a detachable cover arranged to bemounted lying against said partition plane of said track support beam.

Aspect 4: A drive unit according to any preceding aspects, where said atleast one drive wheel and said electric motor are arranged to be mountedin a front section of said track support beam.

Aspect 5: A drive unit according to any preceding aspects, where saidtrack support beam is a skid beam.

Aspect 6: A drive unit according to any preceding aspects, where anoutput shaft 81 of said electric motor is arranged at essentially thesame height of said track support beam as a drive shaft 9 of said tracksupport beam, said drive shaft being arranged to drive said at least onedrive wheel.

Aspect 7: A drive unit according to any preceding aspects, furthercomprising a transmission device 6 7, 8 integrated in said track supportbeam such that the axial main direction of extension of the transmissiondevice is aligned with the output shaft 81 of said electric motor.

Aspect 8: A drive unit according to any preceding aspects, where saidelectric motor is connected to a drive shaft 9 arranged to drive said atleast one drive wheel, via a transmission device comprising a planetarygear 6, a transmission shaft 7 and a bevel gear 8, 8:1, 8:2, to whichsaid drive shaft is connected.

Aspect 9: A drive unit according to aspect 8, where an end of saidtransmission shaft which is directed towards said electric motor isarranged to be connected to said planetary gear and an opposite end ofsaid transmission shaft which is directed towards said drive shaft isarranged to be connected to said bevel gear.

Aspect 10: A drive unit according to any preceding aspects, where saidat least one drive wheel is constituted by a drive wheel pair 28.

Aspect 11: A drive unit according to any preceding aspects, where saidtrack support beam comprises an integrated lubrication system forlubrication.

Aspect 12: A drive unit according to any preceding aspects, where saidtrack support beam comprises an integrated cooling system for cooling.

Aspect 13: A drive unit according to any preceding aspects, where saidtrack support beam is configured for attachment to a chassis beam 45comprising control means for controlling said electric motor.

Aspect 14: A drive unit according to any preceding aspects, where saidelectric motor is configured for attachment to a combustion engine 5 viaa generator for power supply.

Aspect 15: A drive unit according to any preceding aspects, where saidelectric motor is configured for attachment to a combustion engine 5 viaa generator for power supply.

Aspect 16: Tracked vehicle, comprising at least one drive unit accordingto any preceding aspects, where said electric motor is configured to beattached to an energy storage unit for power supply.

Aspect 17: Tracked vehicle according to aspect 16, where said trackedvehicle is a forestry machine.

Aspect 18: Tracked vehicle according to any of aspects 16 or 17, wheresaid tracked vehicle is a forwarder.

Aspect 19: Tracked vehicle according to any of aspects 16 to 18, wheresaid tracked vehicle is hybrid driven.

Below some additional aspects of the tracked vehicle according to thepresent description are listed, which aspects particularly relate to thetransversal partition plane 41.

Aspect 1B: A track support beam 22 for a tracked vehicle 10, configuredto support at least one drive wheel 24, 26, a set of support wheels 23and an endless track 25, wherein the track support beam 22 comprises atransversal partition plane 41 along which the track support beam 22 isconfigured to be divided in a front section 22A and a rear section 22B.

Aspect 2B: A track support beam 22 according to aspect 1B, wherein saidfront 22A and rear 22B sections are configured for removable mounting toeach other along said transversal partition plane 41.

Aspect 3B: A track support beam 22 according to aspect 1B or 2B,comprising an electric motor 3 constituting an electric drive unitarranged to drive said at least one drive wheel 24, 26, wherein theelectric motor 3 is integrated in one of said front 22A and rear 22Bsections constituting a motor comprised section 22A.

Aspect 4B: A track support beam 22 according to aspect 3B, furthercomprising a transmission device 6, 7, 8 integrated in said motorcomprised section 22A of the track support beam 22.

Aspect 5B: A track support beam 22 according to aspect 4B, furthercomprising a lubrication system integrated in said motor comprisedsection 22A of the track support beam 22.

Aspect 6B: A track support beam 22 according to any of the aspects3B-5B, wherein the transversal partition plane 41 is arranged such thatthe motor comprised section 22A is substantially shorter in thelongitudinal direction of the track support beam than what the non-motorcomprised section 22B is, and preferably shorter than a third of theentire length of the track support beam.

Aspect 7B: A track support beam 22 according to any of the aspects1B-6B, wherein the transversal partition plane 41 is configured to giveaccess to an inner space 43, 48 of the motor comprised section 22A bypartition of the track support beam 22 along said transversal partitionplane 41.

Aspect 8B: A track support beam 22 according to aspect 7B, wherein saidinner space 43, 48 entirely or partly accommodates at least one of anelectric motor 3, a transmission device 6, 7, 8 and a lubricationsystem.

Aspect 9B: A track support beam 22 according to aspect 7B or 8B, whereinsaid inner space comprises a chamber 43 constituting a lubricantreservoir.

Aspect 10B:A track support beam 22 according to any of the aspects7B-9B, wherein said inner space 43, 48 is sealable via said partitionplane 41 by means of a detachable sealing cover 19.

Aspect 11B:A track support beam 22 according to aspect 9B and 10B,wherein said sealing cover 19 is configured to detachably seal thechamber 43 constituting lubricant reservoir, wherein the sealing cover19 constitutes a wall of said lubrication reservoir.

Aspect 12B:A track support beam 22 according to any of the aspects9B-11B, wherein said chamber 43 constituting lubricant reservoirconstitutes a lower chamber 43 of said inner space and wherein the innerspace also comprises an upper chamber 48, situated above the lowerchamber 43 and at least partly separated therefrom by means of apartition wall 54, wherein said partition wall comprises one or moreopening or cavities facilitating for lubricant to flow from said upper48 chamber to said lower chamber 43.

Aspect 13B:A track support beam 22 according to aspect 12B, wherein saidelectric motor 3 and/or said transmission device 7, 8, 9 entirely orpartly is arranged in aid upper chamber 48.

Aspect 14B:A track support beam 22 according to any of the aspects1B-13B, wherein the front section 22A and the rear section 22B comprisesflanges 44A, 44B for detachable mounting to each other along saidtransversal partition plane 41.

Aspect 15B:A track support beam 22 according to any of the aspects1B-14B, wherein the front 22A and the rear 22B section of the tracksupport beam 22 are configured for detachable mounting to each other bymeans of a bolt joint 46, 47.

Aspect 16B:A track support beam 22 according to any of the aspects1B-15B, wherein said at least one drive wheel 24, 26 and said set ofsupport wheels 23 are rotatably attached in said track support beam 22,said at least one drive wheel being arranged to drive said endless trackrunning over said at least one drive wheel and said set of supportwheels.

Aspect 17B:A track support beam 22 according to any of the aspects 3B to16B, wherein said electric motor 3 is integrated in said motor section22A of the track support beam 22 in a longitudinal direction of thetrack support beam 22.

Aspect 18B:A track support beam 22 according to any of the aspects 3B to17B, wherein said motor comprised section 22A of the track support beam22 is constituted by the front section 22A.

Aspect 19B:A track support beam 22 according to any of the aspects 1B to18B, further comprising a longitudinal partition plane 40 uncovering aninner space of said track support beam 22 in which an electric motor 3is integrated.

Aspect 20B:A track support beam 22 according to any of the aspects 1B to19B, where said track support beam 22 is a skid beam.

Aspect 21B:A track support beam 22 according to any of the aspects 1B to20B, wherein said track support beam 22 is configured for attachment toa chassis beam 45 comprising control means for controlling of anelectric motor 3 integrated in the track support beam 22.

Aspect 22B:A track assembly, comprising a track support beam 22according to any of the aspects 1B to 21B.

Aspect 23B:A track assembly according to aspect 22B, comprising a tracksupport beam 22 according to aspect 16B and an electric motor 3integrated in the track support beam 22 configured to drive said atleast one drive wheel 24, 26, wherein the track assembly constitutes adrive unit capable of being driven by itself.

Aspect 24B:A tracked vehicle 10, comprising at least one track supportbeam 22 according to any of the aspects 1B-21B.

Aspect 25B:Tracked vehicle 10 according to aspect 24B, where saidtracked vehicle 10 is a forestry machine such as a forwarder.

1. (canceled)
 2. A track support beam for a tracked vehicle, configuredto support at least one drive wheel, a set of support wheels and anendless track, the track support beam comprising a transversal partitionplane along which the track support beam is configured to be divided ina front section and a rear section.
 3. The track support beam accordingto claim 2, wherein said front and rear sections are configured forremovable mounting to each other along said transversal partition plane.4. The track support beam according to claim 2, comprising an electricmotor constituting an electric drive unit arranged to drive said atleast one drive wheel, wherein the electric motor is integrated in oneof said front and rear sections constituting a motor comprised section.5. The track support beam according to claim 4, further comprising atransmission device integrated in said motor comprised section of thetrack support beam.
 6. The track support beam according to claim 5,further comprising a lubrication system integrated in said motorcomprised section of the track support beam.
 7. The track support beamaccording to claim 4, wherein the transversal partition plane isarranged such that the motor comprised section is substantially shorterin the longitudinal direction of the track support beam than what thenon-motor comprised section is, and preferably shorter than a third ofthe entire length of the track support beam.
 8. The track support beamaccording to claim 2, wherein the transversal partition plane isconfigured to give access to an inner space of the motor comprisedsection by partition of the track support beam along said transversalpartition plane.
 9. The track support beam according to claim 8, whereinsaid inner space entirely or partly accommodates at least one of anelectric motor, a transmission device and a lubrication system.
 10. Thetrack support beam according to claim 8, wherein said inner spacecomprises a chamber constituting a lubricant reservoir.
 11. The tracksupport beam according to claim 8, wherein said inner space is sealablevia said partition plane by a detachable sealing cover.
 12. The tracksupport beam according to claim 10, wherein a sealing cover isconfigured to detachably seal the chamber constituting lubricantreservoir, wherein the sealing cover constitutes a wall of saidlubrication reservoir.
 13. The track support beam according to claim 10,wherein said chamber constituting lubricant reservoir constitutes alower chamber of said inner space and wherein the inner space alsocomprises an upper chamber, situated above the lower chamber and atleast partly separated therefrom by a partition wall, wherein saidpartition wall comprises one or more opening or cavities facilitatingfor lubricant to flow from said upper chamber to said lower chamber. 14.The track support beam according to claim 13, wherein at least a portionof at least one of said electric motor and said transmission device isarranged in said upper chamber.
 15. The track support beam according toclaim 2, wherein the front section and the rear section comprise flangesfor detachable mounting to each other along said transversal partitionplane.
 16. The track support beam according to claim 2, wherein thefront and the rear section of the track support beam are configured fordetachable mounting to each other by a bolt joint.
 17. The track supportbeam according to claim 2, wherein said at least one drive wheel andsaid set of support wheels are rotatably attached in said track supportbeam, said at least one drive wheel being arranged to drive said endlesstrack running over said at least one drive wheel and said set of supportwheels.
 18. The track support beam according to claim 4, wherein saidelectric motor is integrated in said motor section of the track supportbeam in a longitudinal direction of the track support beam.
 19. Thetrack support beam according to claim 4, wherein said motor comprisedsection of the track support beam is constituted by the front section.20. The track support beam according to claim 2, further comprising alongitudinal partition plane uncovering an inner space of said tracksupport beam in which an electric motor is integrated.
 21. The tracksupport beam according to claim 2, where said track support beam is askid beam.
 22. The track support beam according to claim 2, wherein saidtrack support beam is configured for attachment to a chassis beamcomprising a control unit for controlling of an electric motorintegrated in the track support beam.
 23. A track assembly, comprisingthe track support beam according to claim
 2. 24. The track assemblyaccording to claim 23, further comprising an electric motor integratedin the track support beam configured to drive said at least one drivewheel, wherein the track assembly constitutes a drive unit capable ofbeing driven by itself.
 25. A tracked vehicle, comprising at least onetrack support beam according to claim
 2. 26. The tracked vehicleaccording to claim 25, where said tracked vehicle is a forestry machinesuch as a forwarder.